Electrolytic device and method of driving electrolytic device

ABSTRACT

An electrolytic device, includes: an electrolysis cell including: a cathode; an anode; a cathode flow path facing the cathode; and an anode flow path facing the anode; a tank including: a first room; a second room; and an opening connecting the first and second rooms, the first and second rooms store a liquid containing at least one ion, the tank forms a level difference so that the first liquid level of the liquid in the first room is higher to the bottom of the second room than the second liquid level of the liquid in the second room, and thus cause an ion in the liquid to move from the first to the second room through the opening; a first flow path connecting an outlet of the cathode flow path and the first room; and a second flow path connecting the second room and an outlet of the anode flow path.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2022-045880, filed on Mar. 22, 2022; theentire contents of which are incorporated herein by reference.

FIELD

Embodiments relate to an electrolytic device and a method of driving anelectrolytic device.

BACKGROUND

In recent years, from the viewpoint of both energy problems andenvironmental problems, it has been desired not only to convertrenewable energy such as solar power into electric energy for use, butalso to convert it into a form that can be stored and transported. Inresponse to this demand, research and development of artificialphotosynthesis technology that produces chemical substances usingsunlight, like photosynthesis by plants, is underway. This technologyhas the potential to store the renewable energy as a storable fuel andis also expected to create value by producing chemical substances thatcan be used as industrial raw materials.

As a device that uses renewable energy to produce chemical substances,there has been known an electrochemical reaction device that includes,for example, a cathode that reduces carbon dioxide (CO₂), generated froma power plant or waste treatment plant and an anode that oxidizes water(H₂O). At the cathode, for example, carbon dioxide is reduced to producecarbon compounds such as carbon monoxide (CO). When such anelectrochemical reaction device is fabricated in a cell form (alsocalled an electrolysis cell), it is considered to be effective tofabricate the device in a form similar to a fuel cell, such as a polymerelectric fuel cell (PEFC), for example. Direct supply of carbon dioxideto a catalyst layer of the cathode enables a carbon dioxide reductionreaction to proceed rapidly.

However, in such a cell form, a problem similar to that of the PEFCarises. In other words, in order to fabricate the electrolysis cell thatis resistant to failure and is durable, it is necessary to keep theresistance of the electrolysis cell low.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating a configuration example of anelectrolytic device 1.

FIG. 2 is a schematic view illustrating a structural example of a tank200.

FIG. 3 is a schematic view illustrating another structural example ofthe tank 200.

FIG. 4 is a schematic view illustrating another structural example ofthe tank 200.

DETAILED DESCRIPTION

An electrolytic device according to an embodiment, including: anelectrolysis cell including: a cathode; an anode; a cathode flow pathfacing on the cathode; and an anode flow path facing on the anode; atank including: a first room; a second room; and an opening connectingthe first room and the second room, the first room and the second roombeing configured to store a liquid containing at least one ion, the tankbeing configured to form a level difference between a first liquid leveland a second liquid level so that a height of the first liquid level ofthe liquid to be stored in the first room relative to a bottom of thesecond room is higher than a height of the second liquid level of theliquid to be stored in the second room relative to the bottom of thesecond room, and thus cause an ion contained in the liquid to move fromthe first room to the second room through the opening; a first flow pathconnecting an outlet of the cathode flow path and the first room; and asecond flow path connecting the second room and an outlet of the anodeflow path.

Hereinafter, there will be explained an embodiment with reference to thedrawings. The drawings are schematic, and dimensions such as a thicknessand a width of each component, for example, are sometimes different fromactual ones. Further, in the embodiment, substantially the samecomponents are denoted by the same reference numerals and symbols, andtheir explanation is sometimes partially omitted.

In this specification, “connection” includes not only direct connectionbut also indirect connection, unless otherwise specified.

FIG. 1 is a schematic view illustrating a configuration example of anelectrolytic device. The electrolytic device illustrated in FIG. 1 is acarbon dioxide electrolytic device.

An electrolytic device 1 illustrated in FIG. 1 includes an electrolysiscell 100, a power supply 150, a tank 200, a cathode supply part 301, andan anode supply part 401.

The electrolysis cell 100 includes an anode 111, an anode flow path 112,an anode current collector 113, a cathode 121, a cathode flow path 122,a cathode current collector 123, and a separator 131. In theelectrolysis cell 100, these members are sandwiched between a pair ofnot-illustrated support plates and further tightened with bolts or othermeans.

The anode 111 is provided between the separator 131 and the anode flowpath 112 to be in contact with them. The anode 111 is an electrode foroxidizing water (H₂O) in an anode solution to produce oxygen (O₂) andhydrogen ions (H⁺), or an electrode for oxidizing hydroxide ions (OH⁻)produced by a reduction reaction of carbon dioxide at the cathode 121 toproduce oxygen and water.

The anode 111 preferably contains a catalyst material capable ofreducing an overvoltage in the above-described oxidation reaction (anodecatalyst material). Examples of such a catalyst material include metalssuch as platinum (Pt), palladium (Pd), and nickel (Ni), alloyscontaining those metals, intermetallic compounds, binary metal oxidessuch as manganese oxide (Mn—O), iridium oxide (Ir—O), nickel oxide(Ni—O), cobalt oxide (Co—O), iron oxide (Fe—O), tin oxide (Sn—O), indiumoxide (In—O), ruthenium oxide (Ru—O), lithium oxide (Li—O), andlanthanum oxide (La—O), ternary metal oxides such as Ni—Co—O, Ni—Fe—O,La—Co—O, Ni—La—O, and Sr—Fe—O, quaternary metal oxides such asPb—Ru—Ir—O and La—Sr—Co—O, and metal complexes such as a Ru complex anda Fe complex.

The anode 111 includes a base material having a structure capable ofmaking a liquid or ions move between the separator 131 and the anodeflow path 112, which is, for example, a porous structure such as a meshmaterial, a punching material, a porous body, or a metal fiber sinteredbody. The base material may be formed of a metal such as titanium (Ti),nickel (Ni), or iron (Fe), or a metal material such as an alloycontaining at least one of these metals (for example, SUS), or may beformed of the above-described anode catalyst material. When an oxide isused as the anode catalyst material, it is preferable to form a catalystlayer by attaching or stacking the anode catalyst material to or on asurface of the base material made of the above-described metal material.The anode catalyst material preferably has nanoparticles, ananostructure, a nanowire, or the like for increasing the oxidationreaction. The nanostructure is a structure with nanoscale irregularitiesformed on the surface of the catalyst material. Further, the oxidationcatalyst does not necessarily have to be provided on the anode 111. Theoxidation catalyst layer provided other than on the anode 111 may beelectrically connected to the anode 111.

The cathode 121 is in contact with the separator 131. To the cathode121, an anode solution and ions are supplied from the separator 131, anda carbon dioxide gas is supplied from the cathode flow path 122. Thecathode 121 is an electrode that causes a reduction reaction of carbondioxide or a reduction reaction of a reduction product to produce carboncompounds (reduction electrode). Examples of the carbon compound includecarbon monoxide (CO), methane (CH₄), ethane (C₂H₆), and so on. Thereduction reaction at the cathode 121 may include a side reaction thatcauses a reduction reaction of water to produce hydrogen (H₂), alongwith the reduction reaction of carbon dioxide.

The cathode 121 includes a gas diffusion layer and a cathode catalystlayer provided on the gas diffusion layer. A porous layer denser thanthe gas diffusion layer may be arranged between the gas diffusion layerand the cathode catalyst layer. The gas diffusion layer is arranged onthe cathode flow path 122 side, and the cathode catalyst layer isarranged on the separator 131 side. The cathode catalyst layer may enterthe gas diffusion layer. The cathode catalyst layer preferably hascatalyst nanoparticles, a catalyst nanostructure, or the like. The gasdiffusion layer is formed of, for example, a carbon paper, a carboncloth, or the like, and may be subjected to a water repellent treatment.The porous layer is formed of a porous body with a smaller pore sizethan the carbon paper or the carbon cloth.

With the application of a moderate water repellent treatment to the gasdiffusion layer, a carbon dioxide gas reaches the cathode catalyst layermainly by gas diffusion. The reduction reaction of carbon dioxide or thereduction reaction of the carbon compound produced by the reductionreaction occur near the boundary between the gas diffusion layer and thecathode catalyst layer, or near the cathode catalyst layer that hasentered the gas diffusion layer.

The cathode catalyst layer is preferably formed of a catalyst materialcapable of reducing an overvoltage in the above-described reductionreaction (cathode catalyst material). Examples of such a materialinclude metals such as gold (Au), silver (Ag), copper (Cu), platinum(Pt), palladium (Pd), nickel (Ni), cobalt (Co), iron (Fe), manganese(Mn), titanium (Ti), cadmium (Cd), zinc (Zn), indium (In), gallium (Ga),lead (Pb), and tin (Sn), metal materials such as alloys containing atleast one of these metals and intermetallic compounds, carbon materialssuch as carbon (C), graphene, CNT (carbon nanotube), fullerene, andketjen black, and metal complexes such as a Ru complex and a Re complex.The cathode catalyst layer can employ various shapes such as a plateshape, a mesh shape, a wire shape, a particle shape, a porous shape, athin film shape, and an island shape.

The cathode catalyst material forming the cathode catalyst layerpreferably has nanoparticles of the above-described metal material, ananostructure of the metal material, a nanowire of the metal material,or a composite body in which nanoparticles of the above-described metalmaterial are supported on a carbon material such as carbon particles, acarbon nanotube, or graphene. Applying catalyst nanoparticles, acatalyst nanostructure, a catalyst nanowire, a catalyst nano-supportstructure, or the like as the cathode catalyst material makes itpossible to increase the reaction efficiency of the reduction reactionof carbon dioxide at the cathode 121.

The anode 111 and the cathode 121 can be connected to the power supply150. Examples of the power supply 150 are not limited to ordinary systempower supplies or batteries, but may include a power source thatsupplies power generated by renewable energy such as solar cells or windpower generation. The use of renewable energy is also environmentallypreferable in terms of effective use of carbon dioxide. The power supply150 may further include a power controller that controls a voltagebetween the anode 111 and the cathode 121 by adjusting output of theabove-described power supply. The power supply 150 may be providedoutside the electrolytic device 1.

The anode flow path 112 faces the anode 111. The anode flow path 112 hasa function of supplying an anode solution to the anode 111.

The anode solution preferably contains at least water (H₂O). The liquidmay contain carbon dioxide (CO₂). The liquid does not need to containcarbon dioxide (CO₂) because carbon dioxide (CO₂) is supplied from thecathode flow path 122.

As the anode solution, an aqueous solution containing metal ions(electrolytic solution) can be used. Examples of the aqueous solutioninclude aqueous solutions containing phosphate ions (PO₄ ²⁻), borateions (BO₃ ³⁻), sodium ions (Nat), potassium ions (K⁺), calcium ions(Ca²⁺), lithium ions (Li⁺), cesium ions (Cs⁺), magnesium ions (Mg²⁺),chloride ions (Cl⁻), hydrogen carbonate ions (HCO₃ ⁻), and so on.Besides, aqueous solutions containing LiHCO₃, NaHCO₃, KHCO₃, CsHCO₃,phosphoric acid, boric acid, and so on may also be used.

The anode flow path 112 is provided on a surface of a flow path plate114. The flow path plate 114 is to supply the anode solution, which isan electrolytic solution, to the anode 111, and has a groove (recessedportion) in its surface in which the anode flow path 112 is formed. Asthe material of the flow path plate 114, it is preferable to use amaterial having low chemical reactivity and high conductivity. Examplesof such a material include metal materials such as Ti and SUS, carbon,and so on. The anode flow path 112 may be provided at the anode currentcollector 113. Further, the material of the flow path plate 114 containsa material having low chemical reactivity and no conductivity, forexample. Examples of such a material include insulating resin materialssuch as an acrylic resin, polyether ether ketone (PEEK), and afluorocarbon resin. The flow path plate 114 has an inlet port and anoutlet port of the anode flow path 112 and screw holes for tightening,which are not illustrated.

The flow path plate 114 is mainly formed of one member, but may beformed of different members to be formed by stacking them. Further, asurface treatment may be applied to a portion or all of the surface, tothereby provide a hydrophilic or water-repellent function.

The anode flow path 112 has an inlet and an outlet, and the anodesolution is supplied from the anode supply part 401 through the inlet,and the anode solution is discharged through the outlet. The anodesolution flows through inside the anode flow path 112 so as to be incontact with the anode 111.

The anode current collector 113 is electrically connected to the anode111. The anode current collector 113 is in contact with the surface ofthe flow path plate 114 on the side opposite to the anode flow path 112.The anode current collector 113 preferably contains a material havinglow chemical reactivity and high conductivity. Examples of such amaterial include metal materials such as Ti and SUS, carbon, and so on.

The cathode flow path 122 faces the cathode 121. The cathode flow path122 has a function of supplying a fluid containing carbon dioxide(cathode gas) to the cathode 121. The fluid containing carbon dioxidemay contain steam by being humidified. The compound produced by thereduction reaction is mainly discharged from the cathode flow path 122.The compound produced by the reduction reaction varies depending on thetype of reduction catalyst, or other factors. Along with such a gasproduct, vapor or moisture obtained by dew condensation of steamcontained in the humidified carbon dioxide gas is discharged from thecathode flow path 122.

The cathode flow path 122 is provided on a surface of a flow path plate124. The flow path plate 124 has a groove (recessed portion) in itssurface in which the cathode flow path 122 is formed. As the material ofthe flow path plate 124, it is preferable to use a material having lowchemical reactivity and high conductivity. Examples of such a materialinclude metal materials such as Ti and SUS, carbon, and so on. Further,the material of the flow path plate 124 contains a material having lowchemical reactivity and no conductivity, for example. Examples of such amaterial include insulating resin materials such as an acrylic resin,polyether ether ketone (PEEK), and a fluorocarbon resin. The flow pathplate 124 has not-illustrated screw holes for tightening. Further, anot-illustrated packing is sandwiched at the front and the back of eachof the flow path plates as necessary. The cathode flow path 122 may beprovided at the cathode current collector 123.

The cathode flow path 122 has an inlet and an outlet, and the cathodegas such as carbon dioxide is supplied from the cathode supply part 301through the inlet, and the fluid containing the cathode gas isdischarged through the outlet. The cathode gas flows through inside thecathode flow path 122 so as to be in contact with the cathode 121.

The cathode flow path 122 may have a land in contact with the cathode121 for electrical connection with the cathode 121. The shape of thecathode flow path 122 is not particularly limited as long as it iscontinuously connected, and examples of the shape include a serpentinestructure with a bent elongated flow path, and so on. As a result, thecathode gas flows uniformly on the surface of the cathode 121, so that auniform reaction can be performed at the cathode 121, which ispreferable.

The cathode gas may be supplied in a dry state. When the cathode gas isa carbon dioxide gas, the concentration of carbon dioxide in the cathodegas supplied from the cathode supply part 301 to the cathode flow path122 does not have to be 100%. The gas containing carbon dioxidedischarged from various facilities can also be used as the cathode gas.

The flow path plate 124 is mainly formed of a single member, but may beformed of different members to be formed by stacking them. Further, asurface treatment may be applied to a portion or all of the surface, tothereby provide a hydrophilic or water-repellent function.

The cathode current collector 123 is electrically connected to thecathode 121 of the electrolysis cell 100. The cathode current collector123 preferably contains a material having low chemical reactivity andhigh conductivity. Examples of such a material include metal materialssuch as Ti and SUS, carbon, and so on.

The separator 131 is arranged so as to separate the anode 111 and thecathode 121. The separator 131 includes an ion exchange membrane capableof making ions move between the anode 111 and the cathode 121 andseparating the anode 111 and the cathode 121. As an example of the ionexchange membrane, for example, cation exchange membranes such as Nafionand Flemion, and anion exchange membranes such as Neosepta, Selemion,and Sustainion can be used. When an alkaline solution is used as theelectrolytic solution and moving of OH⁻ is mainly assumed, the separator131 is preferably formed of the anion exchange membrane. Further, theion exchange membrane may be formed by using a membrane having ahydrocarbon basic structure or a membrane having an amine group.However, besides the ion exchange membrane, a salt bridge, a glassfilter, a porous polymer membrane, a porous insulating material, or thelike may be applied to the separator 131 as long as the material iscapable of making ions move between the anode 111 and the cathode 121.However, when gas distribution occurs between the anode 111 and thecathode 121, a circular reaction due to reoxidation of a reductionproduct sometimes occurs. Therefore, it is preferable to have less gasexchange between the anode 111 and the cathode 121. Therefore, careshould be taken when using a porous thin membrane as the separator 131.

Next, an example of a method of driving the electrolysis cell 100 isexplained. Here, the case of producing carbon monoxide as the carboncompound, is mainly explained but the carbon compound as a reductionproduct of carbon dioxide is not limited to carbon monoxide.

First, a reaction process in the case of mainly oxidizing water (H₂O) toproduce hydrogen ions (H⁺) is explained. When the current is suppliedbetween the anode 111 and the cathode 121 from the power supply 150, theoxidation reaction of water (H₂O) occurs at the anode 111 in contactwith the anode solution. Specifically, as illustrated in Expression (1)below, H₂O contained in the anode solution is oxidized to produce oxygen(O₂) and hydrogen ions (H⁺).

2H₂O→4H⁺+O₂+4e ⁻  (1)

H⁺ produced at the anode 111 moves through the electrolytic solutionpresent in the anode flow path 112 and the separator 131 to reach nearthe cathode 121. Electrons (e⁻) based on the current supplied to thecathode 121 from the power supply 150 and H⁺ that has moved near thecathode 121 cause the reduction reaction of carbon dioxide.Specifically, as illustrated in Expression (2) below, carbon dioxidesupplied to the cathode 121 from the cathode flow path 122 is reduced toproduce carbon monoxide. Further, hydrogen is produced by hydrogen ionsreceiving electrons, as illustrated in Expression (3) below. At thistime, hydrogen may be produced simultaneously with carbon monoxide.

CO₂+2H⁺+2e ⁻→CO+H₂O  (2)

2H⁺+2e ⁻→H₂  (3)

Next, a reaction process in the case of mainly reducing carbon dioxide(CO₂) to produce hydroxide ions (OH⁻) is explained. When the current issupplied between the anode 111 and the cathode 121 from the power supply150, water (H₂O) and carbon dioxide (CO₂) are reduced near the cathode121 to produce carbon monoxide (CO) and hydroxide ions (OH⁻), asillustrated in Expression (4) below. Further, hydrogen is produced bywater receiving electrons as illustrated in Expression (5) below. Atthis time, hydrogen may be produced simultaneously with carbon monoxide.The hydroxide ions (OH⁻) produced by these reactions diffuse near theanode 111, and as illustrated in Expression (6) below, the hydroxideions (OH) are oxidized to produce oxygen (O₂).

2CO₂+2H₂O+4e ⁻→2CO+4OH⁻  (4)

2H₂O+2e ⁻→H₂±2OH⁻  (5)

4OH⁻→2H₂O+O₂+4e ⁻  (6)

The electrolysis cell 100 can not only specialize in the reduction ofcarbon dioxide, but can also produce reduction products and hydrogen atan arbitrary ratio where, for example, carbon monoxide and hydrogen areproduced at a ratio of 1:2, to produce methanol by a subsequent chemicalreaction.

Since hydrogen is an inexpensive and readily available raw material fromwater electrolysis and fossil fuels, the ratio of hydrogen does not needto be large. From these viewpoints, the ratio of carbon monoxide tohydrogen is at least 1 or more, and preferably 1.5 or more, which ispreferable from economic and environmental aspects.

The electrolytic device in the embodiment is not limited to the carbondioxide electrolytic device, and may be a nitrogen electrolytic device,for example. In the case of the nitrogen electrolytic device, thecathode 121 can reduce a nitrogen (N₂) gas to produce ammonia. For theother configuration of the nitrogen electrolytic device, theconfiguration of the carbon dioxide electrolytic device can be used asappropriate.

In the electrolysis cell 100, there has been known a phenomenon in whichpotassium (K⁺) ions in the electrolytic solution circulating on theanode flow path 112 side move to the cathode flow path 122 side, and theK⁺ ions flow out to the outside of the cell together with vapor,moisture generated at the cathode 121, or the like from the outlet ofthe cathode flow path 122, causing a decrease in the concentration ofthe electrolytic solution. When the concentration of the electrolyticsolution circulating on the anode 111 side decreases, the resistance ofthe electrolysis cell 100 increases, causing problems such asdegradation of the performance of the electrolysis cell 100 during along continuous operation. In contrast to this, it is conceivable to usea pump to return the liquid that has collected in a cathode dischargeliquid recovery bottle, called a trap, located on the outlet side of thecathode flow path 122, to an electrolytic solution tank that stores theelectrolytic solution, which is connected to the anode flow path 112.This makes it possible to return the K⁺ ions contained in the cathodedischarge liquid to the electrolytic solution having a decreasedconcentration, and thus, the decrease in the concentration of theelectrolytic solution can be hindered.

However, when the trap is used, the trap, the pump for moving the liquidfrom the trap to the electrolytic solution tank, and the like arerequired, the system around the electrolysis cell 100 becomescomplicated, and power for driving the pump is also required. Further,the discharge rate of the liquid to be discharged from the cathode flowpath 122 is slower than an electrolytic solution circulation rate on theanode flow path 112 side, and thus, the timing of transferring theliquid that has collected in the trap to the electrolytic solution tankbecomes intermittent. In addition, it has been known that theconcentration of K⁺ ions in the cathode discharge liquid is higher thanthe concentration of K⁺ ions in the electrolytic solution. Therefore, ahigh-concentration K⁺ ion-containing liquid is intermittently droppedinto the electrolytic solution tank. As a result, in this case, it takestime for the K⁺ ions to diffuse in the electrolytic solution tank tomake the concentration of K⁺ ions uniform. It is preferable to have amore efficient mechanism that avoids such a decrease in theconcentration of the electrolytic solution.

In contrast to this, the electrolytic device 1 in the embodimentincludes the tank 200, and does not include any traps and any pumps formoving liquid from the trap to the electrolytic solution tank. FIG. 2 isa schematic view illustrating a structural example of the tank 200. Thetank 200 includes an room 201, an room 202, a supply flow path 204, adischarge flow path 205, a supply flow path 206, a discharge flow path207, and a discharge flow path 208.

The room 201 and the room 202 can store a liquid containing the anodesolution. The container forming the room 201 and the room 202 may bemade of glass, resin, metal, or the like. This container is a containerhaving high gas and liquid airtightness. When the container is made ofmetal, an insulating coating is preferably applied inside in order toavoid leakage currents due to electrical conduction through the anodesolution. The insulating coating may be resin, glass, or rubber, and ispreferably highly durable. The container may be provided with waterlevel sensors for measuring the heights of the liquid level of theliquid stored at one or several places in the container. Further, thecontainer may be provided with sensors for measuring the ionconcentration or conductivity of the liquid at one or several places inthe container. Further, the container may be provided with sensors formeasuring the pressure or temperature in the container at one or severalplaces. The operation of the electrolytic device 1 may be controlled bya controller or the like with reference to the values detected by thesesensors.

The volume of the container is preferably large enough to hold the anodesolution for operating the electrolytic device 1 and the condensedwater, and may be, for example, a volume of 1 L to 100 L, but the volumeis not limited to this range. The shape of the container is notparticularly limited, but may be spherical, cylindrical, or rectangular,for example.

At least one room may be further provided between the room 201 and theroom 202. It is preferable that the heights of the bottoms of theserooms should be lowered gradually. It is further preferable that theanode solution should be always present in all of these rooms.

Further, a pipe for recovering gas may be connected to each of the topsof a plurality of the rooms. Thereby, even if the total amount of liquidin the container decreases or increases for some reason, the gas fromthe cathode flow path 122 and the gas from the anode flow path 112 donot mix easily, and gas products can be recovered while maintaining asafe state.

A partition 203 is provided between the room 201 and the room 202, andseparates the room 201 from the room 202. The partition 203 includes atleast one opening 203 a connecting the room 201 and the room 202. Anypumps are not formed in the middle of the opening 203 a. The material ofthe partition 203 may be a semipermeable membrane, a polymer membrane, aliquid junction, or a porous material that allows liquid to passtherethrough but does not allow gas to pass therethrough, and may be,for example, a glass filter impregnated with liquid. Further, an ionexchange membrane may be used, and for example, a cation exchangemembrane such as Nafion or Flemion can be used. The liquid junction maybe, for example, a sintered glass layer, a cellulose layer, pulp,absorbent cotton, an animal semipermeable membrane such as fish skin, anion exchange membrane, agar, a solution having a coagulated crystalstructure, such as gelatin, or the like. A plurality of the openings 203a may be provided.

The opening 203 a allows liquid to pass therethrough but does not allowgas to pass therethrough. This makes it possible to spatially separatethe gas component (for example, CO, CO₂, or hydrogen (H₂) gas) thatcomes out with the fluid discharged from the outlet of the cathode flowpath 122 and the gas component (for example, oxygen (O₂) or CO₂ gas)that comes out with the electrolytic solution discharged from the outletof the anode flow path 112. Thereby, valuable products (for example, COor H₂ gas), which are products of a carbon dioxide electrolysis cell,can be recovered separately from the liquid, and further, the H₂ gas andthe O₂ gas described above do not mix, and thus it is effective forsafety.

The room 201 and the room 202 may be asymmetrical in shape with thepartition 203 as a boundary. The two spaces created by the wall providedinside the container may have the same shape and volume, but may havedifferent shapes and volumes. The volume of the room 201 is preferablysmaller than the volume of the room 202, and further, an top 201 a ofthe room 201 may be higher in height relative to a bottom 202 b of theroom 202 than an top 202 a of the room 202. Further, a bottom 201 b ofthe room 201 may be inclined so as to be lowered toward the room 202 inorder to promote the movement of liquid from the room 201 to the room202.

The supply flow path 204 connects the room 201 and the outlet of thecathode flow path 122. The electrolytic device 1 can supply the fluidcontaining the cathode gas supplied from the cathode flow path 122 tothe room 201 via the supply flow path 204. The supply flow path 204 ispreferably provided at a position closer to the top 201 a than thebottom 201 b of the room 201. As a result, the liquid from the cathodeflow path 122 collects in the bottom of the container, and the gasproduct from the cathode flow path 122 collects in the top of thecontainer. FIG. 2 illustrates, as one example, the supply flow path 204provided in the top 201 a.

The discharge flow path 205 is connected to the room 201. Theelectrolytic device 1 can discharge gaseous reduction products in theroom 201 from the room 201 via the discharge flow path 205. Thedischarge flow path 205 is preferably provided at a position closer tothe top 201 a than the bottom 201 b of the room 201. FIG. 2 illustrates,as one example, the discharge flow path 205 provided in the top 201 a.

The supply flow path 206 connects the room 202 and the outlet of theanode flow path 112. The electrolytic device 1 can supply the fluidcontaining the anode solution supplied from the anode flow path 112 tothe room 202 via the supply flow path 206. The supply flow path 206 maybe provided at a position closer to the top 202 a than the bottom 202 bof the room 202, or may be provided at a position closer to the bottom202 b than the top 202 a of the room 202. FIG. 2 illustrates, as oneexample, the supply flow path 206 provided in the top 202 a.

The discharge flow path 207 is connected to the room 202. Theelectrolytic device 1 can discharge gaseous oxidation products suppliedinto the room 202 from the room 202 via the discharge flow path 207. Thedischarge flow path 207 may be provided at a position closer to the top202 a than the bottom 202 b of the room 202, or may be provided at aposition closer to the bottom 202 b than the top 202 a of the room 202.FIG. 2 illustrates, as one example, the discharge flow path 207 providedin the top 202 a.

The discharge flow path 208 connects the room 202 and the anode supplypart 401. The electrolytic device 1 can discharge the liquid containingthe anode solution in the room 202 from the room 202 to the anode supplypart 401 via the discharge flow path 208. The discharge flow path 208 ispreferably provided at a position closer to the bottom 202 b than thetop 202 a of the room 202. FIG. 2 illustrates, as one example, thedischarge flow path 208 provided in a side portion 202 c of the room202.

The supply flow path 204, the discharge flow path 205, the supply flowpath 206, the discharge flow path 207, and the discharge flow path 208each are a pipe. The pipe is formed by using a material applicable tothe container, for example.

The cathode supply part 301 is connected to the inlet of the cathodeflow path 122. The cathode supply part 301 can supply the cathode gas tothe cathode flow path 122. In the case of the carbon dioxideelectrolytic device, the cathode supply part 301 can supply a cathodegas containing a carbon dioxide gas to the cathode flow path 122. In thecase of the nitrogen electrolytic device, the cathode supply part 301can supply a cathode gas containing nitrogen to the cathode flow path122. The cathode supply part 301 includes, for example, a tank thatstores the cathode gas, a mass flow controller that adjusts the flowrate of the cathode gas to be supplied from the tank to the cathode flowpath 122, and so on. The supply of the cathode gas by the cathode supplypart 301 may be controlled by a controller or the like according to adetection signal from water level sensors, pressure sensors, temperaturesensors, sensors that measure the ion concentration or conductivity of aliquid, or the like provided in the container forming the room 201 andthe room 202.

The anode supply part 401 connects the discharge flow path 208 and theinlet of the anode flow path 112. The anode supply part 401 can supplythe fluid containing the anode solution discharged from the dischargeflow path 208 to the anode flow path 112. This allows the anode solutionto circulate. The anode supply part 401 includes, for example, a pump.The flow rate of the liquid containing the anode solution to be suppliedto the anode 111 can be adjusted by the pump. The supply of the liquidby the anode supply part 401 may be controlled by a controller or thelike according to a detection signal from water level sensors, pressuresensors, temperature sensors, sensors that measure the ion concentrationor conductivity of a liquid, or the like provided in the containerforming the room 201 and the room 202.

Next, an example of a method of driving the tank 200 is explained. Whenthe electrolytic solution that has moved to the cathode flow path 122side is supplied from the supply flow path 204 together with the cathodegas, the fluid containing the liquid and the gas generated on thecathode 121 side is pushed by the pressure of a raw material gassupplied to the cathode 121 side to the room 201. In the room 201,gas-liquid separation occurs due to the effect of gravity or the like.The separated liquid generated on the cathode 121 side containing metalions is stored in the bottom of the room 201. On the other hand, aliquid having a substantially constant water level is present in theroom 202. The electrolytic device 1 is driven in a manner that when thefluid containing the anode solution is supplied to the room 202 from thesupply flow path 206 and the electrolytic solution that has moved to thecathode flow path 122 side is supplied to the room 201 from the supplyflow path 204 together with the cathode gas, a level difference betweena liquid level 211 and a liquid level 212 is formed so that the heightof the liquid level 211 of the liquid stored in the room 201 relative tothe bottom 202 b of the room 202 is higher than the height of the liquidlevel 212 of the liquid stored in the room 202 relative to the bottom202 b of the room 202. This causes ions such as K⁺ ions contained in theelectrolytic solution to move from the room 201 to the room 202 throughthe opening 203 a.

This allows, for example, the liquid having a high K⁺ ion concentrationdischarged from the outlet of the cathode flow path 122 and theelectrolytic solution circulating on the anode flow path 112 side to mixtogether through the opening 203 a. Thereby, the K⁺ ions diffuse in theelectrolytic solution, and thus, a large concentration gradient does notoccur, the time until the concentration of the K⁺ ions becomes uniformcan be significantly shortened, and the state where the electrolyticsolution in the room 202 has a high concentration can be maintained.Further, the device configuration can be simplified, and thus, theinstallation area of the device can be made smaller. Further, theconfiguration of the tank 200 does not require the trap or the pump formoving liquid from the trap to the electrolytic solution tank, so thatit is possible to reduce the amount of power required to operate thepump.

The structure of the tank 200 is not limited to the structural exampleillustrated in FIG. 2 . FIG. 3 and FIG. 4 are schematic viewsillustrating another structural example of the tank 200.

A tank 200 illustrated in FIG. 3 is different from the tank 200illustrated in FIG. 2 in that the opening 203 a is formed by using apipe 231. The pipe 231 connects the room 201 and the room 202. The pipe231 may be formed by using a material applicable to the container, forexample.

A valve controlled by an external signal may be provided in the middleof the pipe 231. The opening and closing of the valve is controlled by acontroller or the like according to a detection signal from water levelsensors, pressure sensors, temperature sensors, sensors that measure theion concentration or conductivity of a liquid, or the like provided inthe container.

Further, the tank 200 illustrated in FIG. 3 is different from the tank200 illustrated in FIG. 2 in that the level difference between theliquid level 211 and the liquid level 212 is formed by making the bottom201 b higher in height relative to the bottom 202 b than the bottom 202b.

A tank 200 illustrated in FIG. 4 is different from the tank 200illustrated in FIG. 2 in that the opening 203 a is formed in a partition232 that does not allow liquid or gas to pass therethrough. The materialof the partition 232 may be, for example, glass, resin, or metal. Whenthe material of the partition 232 is metal, the partition 232 and theoutside of the container are preferably electrically insulated. Thethickness of the partition 232 is not particularly limited as long as itis strong enough to withstand the pressure difference in the internalspace of the container. The thickness of the partition 232 may be, forexample, 1 mm to 50 cm, but is not limited to this range.

The opening 203 a illustrated in FIG. 4 is provided at a position closerto the bottom 201 b of the room 201 and the bottom 202 b of the room 202than the top 201 a of the room 201 and the top 202 a of the room 202,respectively. The opening 203 a may have a polygonal shape such as atriangle or a circle, or the shape of the opening 203 a may be acombination thereof. The opening 203 a preferably has a shape that doesnot hinder the movement of liquid, but the circumference of the opening203 a may be flat or may have a protrusion provided thereon.

The opening 203 a preferably has a size that does not hinder themovement of liquid, and the size may be, for example, 1 mm to 10 cm, butis not limited to this range.

The number of openings 203 a per unit area is preferably a value thatdoes not hinder the movement of liquid, and more preferably a value thatcan maintain the strength of the partition 203.

The above embodiment has been presented by way of example only, and isnot intended to limit the scope of the inventions. Indeed, the aboveembodiment may be embodied in a variety of other forms; furthermore,various omissions, substitutions, and changes in the form of theembodiment described herein may be made without departing from thespirit of the inventions. The accompanying claims and their equivalentsare intended to cover such forms or modifications as would fall withinthe scope and spirit of the inventions.

1. An electrolytic device, comprising: an electrolysis cell comprising: a cathode; an anode; a cathode flow path facing on the cathode; and an anode flow path facing on the anode; a tank comprising: a first room; a second room; and an opening connecting the first room and the second room, the first room and the second room being configured to store a liquid containing at least one ion, the tank being configured to form a level difference between a first liquid level and a second liquid level so that a height of the first liquid level of the liquid to be stored in the first room relative to a bottom of the second room is higher than a height of the second liquid level of the liquid to be stored in the second room relative to the bottom of the second room, and thus cause an ion contained in the liquid to move from the first room to the second room through the opening; a first flow path connecting an outlet of the cathode flow path and the first room; and a second flow path connecting the second room and an outlet of the anode flow path.
 2. The device according to claim 1, wherein the tank comprises a partition provided between the first and second rooms and having the opening.
 3. The device according to claim 1, wherein the tank comprises a pipe having the opening.
 4. The device according to claim 1, wherein the tank does not comprise any pumps in the middle of the opening.
 5. The device according to claim 1, wherein a bottom of the first room is higher than the bottom of the second room.
 6. The device according to claim 1, wherein the cathode is configured to reduce carbon dioxide to produce a carbon compound.
 7. The device according to claim 1, wherein the cathode is configured to reduce nitrogen to produce ammonia.
 8. The device according to claim 1, wherein the at least one ion includes a potassium ion.
 9. A method of driving an electrolytic device, the electrolytic device comprising: an electrolysis cell comprising: a cathode; an anode; a cathode flow path facing on the cathode; and an anode flow path facing on the anode; a tank comprising: a first room; a second room; and an opening connecting the first room and the second room, the first room and the second room being configured to store a liquid containing at least one ion; a first flow path connecting an outlet of the cathode flow path and the first room; and a second flow path connecting the second room and an inlet of the anode flow path, the method comprising: forming a level difference between a first liquid level and a second liquid level so that a height of the first liquid level of the liquid to be stored in the first room relative to a bottom of the second room is higher than a height of the second liquid level of the liquid to be stored in the second room relative to the bottom of the second room, and thus causes an ion contained in the liquid to move from the first room to the second room through the opening.
 10. The method according to claim 9, wherein the tank comprises a partition provided between the first and second rooms and having the opening.
 11. The method according to claim 9, wherein the tank comprises a pipe having the opening.
 12. The method according to claim 9, wherein the tank does not comprises any pumps in the middle of the opening.
 13. The method according to claim 9, wherein a bottom of the first room is higher than the bottom of the second room.
 14. The method according to claim 9, wherein the cathode reduces carbon dioxide to produce carbon compounds.
 15. The method according to claim 9, wherein the cathode reduces nitrogen to produce ammonia.
 16. The method according to claim 9, wherein the at least one ion includes a potassium ion. 